1. Field of the Invention
The present invention relates to a method and apparatus for removing plated metal, particularly from steel sheet scraps, for example, removing zinc from galvanized steel sheet scraps.
2. Description of the Prior Art
When using galvanized steel sheet scraps such as automobile scraps and press scraps for steel materials, it is desirable to remove the plated zinc from the galvanized steel sheet scraps, because zinc oxide shortens the life of a smelting furnace.
One example of a prior art method for removing zinc from galvanized steel sheets is disclosed in Japanese Patent Publication SHO 61-23858, though the galvanized steel sheets are not automobile steel sheet scraps. With that method, the galvanized steel sheets are heated in a furnace under reduced pressure to evaporate the plated metal and then the evaporated metal is retrieved with a collector.
However, if that prior art method is used to remove zinc from galvanized steel sheet scraps from automobiles, zinc can not be removed with great efficiency. This is because scraps brought from car shredders usually have machine oil and press oil adhered to the scraps and often contain resin parts. When such scraps are heated, the organic material evaporates to form layers of fireproofing compounds such as ZnCl.sub.2, ZnS, and ZnSO.sub.4 on the surfaces of the scraps, which suppresses the evaporation of zinc.